"Gma" investigators. Those popular fitness bands, the wearable tech gadgets are all the rage for those who want to keep close tabs on their health. How much are they moving, eating and sleeping, sho iing Mara schiavocampo and Dr. Richard Besser checked them out. Good morning. These keep activity and calorie burns, factoring in height, weight and gender to increase accura accuracy. They say they have good estimates, but how good are they? We put three of the bands up to a "Gma" investigators challenge. Reporter: They track it all, calories, steps, even sleep. But a 2014 Iowa state study found the calorie burn estimates have about a 10 to 15% margin of error. Reporter: And they're not cheap, we put three popular bands, one to $200 up to a challenge, the fitbit flex, the jawbone, and the 351. We wore all three giving them time to get used to the bodies and fitness routines. To see how much activity. And we headed to the hospital for special surgery. This metabolic cart is our gold standard calorie counter. How accurate? Very accurate, it's measuring your exhaled air. What you're burning. To make it interesting, we threw in a $20 pedometer and calorie tracker. Hooked on the breathing masks. Put on the mouthpiece. Reporter: And ran for six minutes. According to the cart, we burned -- 89 calories total. That was 65. Reporter: And are entered into the fitbit and jawbone apps,ed a justing accordingly. Mine was exact, Dr. Besser's of a by two. Four to six, the jawbones, 10 to 15, the timeex, more. And using their own algorithm to count the steps, even though we were wearing all three all the time, different daily step count totals. We took them to the park, walking exactly 100 steps. Comparing their Numbers -- one, two, three -- To our count, the old fashioned way. A hundred. After all three, the fitbit was the only device to hit the 100 step mark. Another trial? 125. The jawbean, close to 100, the closest? 10 is 1. The timex, was off. I wondered if I didn't sync it right. They were different from the bands. My monitor, 107. Telling ABC news, different http://www.purelyhealth.org/biotrust-pro-x10/protein-drinks/ factors could give variance. But fitbit said, while there's a small difference, ultimately the success of our products comes from empowering users to accurately see their overall health. We found they don't give you laboratory precision consistently, but they're a great tool to keep check with your daily activity. Keep in mind the Readings may not be 100% accurate all the time. And the cheap timex pedometer, doesn't have the bells and whistles, but to get an idea of the activity, it was a great low-cost option. I wondered and hoped that mine was accurate. I have been lazy today, and I get up and take a walk. It will vary with the activities. Say you're doing something else. Biking, I'm doing this so I can get -- That's cheating. You're only compete cheating yourself. I ride my bike, it doesn't pick it up so well. If you do my thing, it will. Get bored, sit and do this. We didn't get into the sleep thing. Also shows you -- wow, it is possible http://www.purelyhealth.org/biotrust-pro-x10/whey-protein/ to stay up for 24 hours straight. Yep. I think the sleep part is really interesting. Thanks to the team. Great. Thank you. Thank you both. Coming up, a new warning

This transcript has been automatically generated and may not be 100% accurate.